Arid northeastern Brazil

The basement complex for the Patagonian desert and arid northeastern Brazil is formed by metamorphosed Precambrian rocks. Landscapes are characterized by level erosion surfaces of different ages. The landscape is dissected by a large number of valleys. Large depressions are filled with marine and continental beds of sedimentary rocks. Rocks in the Andean system, that stretches the entire length of the west side of the continent, vary greatly. Many depressions are filled with sediments. In addition, many active volcanoes are responsible for periodic lava flows and the deposition of volcanic ash. East of the Andes, the land surface is level and slopes towards the Atlantic Ocean. Broad depressions contain saline or sodic soils. 

Auler, A.S. Smart, P.L. 2003. The influence of bed-rock derived acidity in the development of surface and underground karst evidence from the Precambrian carbonates of semi-arid northeastern Brazil , Earth Surface Processes and Landforms, 28, 157-168... 

Tiessen, H., Salcedo, I. H., and Sampaio, E. V. S. B. (1992). Nutrient and soil organic matter d)mamics under shifting cultivation in semi-arid northeastern Brazil. Agri. Ecosystems Environ. 38, 139-151. 

Cartaxo, S. L., de Almeida Souza, M. M., de Albuquerque, U.P. (2010). Medieinal plants with bioprospecting potential used in semi-arid northeastern Brazil. J. Ethnopharmacoi, 131(2), 326-342. 

Atkinson TC, Rowe PJ (1992) Applications of dating to denudation chronology and landscape evolution. In Uranium-series disequilibriiun Applications to Earth, Marine and Enviromnental Sciences, Ivanovich M, Harmon RS (eds) Oxford University Press, Oxford, p 669-703 Auler AS, Smart PL (2001) Late Quaternary paleoclimate in semiarid Northeastern Brazil from U-series dating of travertines and water table speleothems. Quat Res 55 159-167 Ayliffe LK, Marianelh PC, Moriarty KC, Wells RT, McCulloch MT, Mortimer GE, Hellstrom JC (1998) 500 ka precipitation record from southeastern Australia Evidence for interglacial relative aridity. Geology 26 147-150... 

Extensive, horizontal sandstone plateaus occur in tropical shield areas. Well-known examples are the Precambrian Roraima sandstone formations on the Guiana Shield and the Voltaian sandstone formations in Western Africa. Major occurrences of consolidated sands are found in Northern Africa, in Guyana and Surinam, eastern Peru, northeastern Brazil and in Liberia (western Africa). These sandstone formations have a history of tropical weathering in common they all have a deep weathering mantle of bleached, white sands that are very rich in quartz, poor in clay and excessively drained. Electrolyte contents differ by region In arid and semi-arid areas where evaporation exceeds precipitation, salts and carbonates may accumulate at or near the surface of the soil. 

Alves, R. R. N., Neto, N. A. L., Brooks, S. E., and Albuquerque, U. P. (2009). Commercialization of animal-derived remedies as complementary medicine in the semi-arid region of Northeastern Brazil. J. Ethnopharmacol. 124, 600-608. 

Rivers and shallow groundwater are often saline in arid or semiarid regions. Examples are common in northeastern Brazil in crystalline rocks, remote from the sea, and in regions where no marine transgression has occurred for 100 million years. Hence, evaporation was for a long time... 

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